Nice technique with the wing covering.

You need to send jofrost a pm with a link to your thread to join Funbuild 5.

Len

Originally Posted by LenBFP

Nice technique with the wing covering.

You need to send jofrost a pm with a link to your thread to join Funbuild 5.

Len

Got it ( Hoping we see some more join in , especially after all the hoopla about having a "Multi-Engine" Funbuild ) Maybe some are intimidated by multiple engine setups I know if I wasn't so wrapped up with various "life" issues , I'd use this opportunity to complete my much neglected B25 ( 60% done... )

A great informative build here !


-John

Originally Posted by jofrost

Got it ( Hoping we see some more join in , especially after all the hoopla about having a "Multi-Engine" Funbuild ) Maybe some are intimidated by multiple engine setups I know if I wasn't so wrapped up with various "life" issues , I'd use this opportunity to complete my much neglected B25 ( 60% done... )

A great informative build here !


-John

Might want to post an invitation on some of the other forums. I'd like to see some multi engine EDF's. Lot's of activity in the electric jets forums. Multiengine sport scale subjects are common on the scratchbuilt foamies forum. I'm sure there are folks in the warbird forum interested in doing a B-25 or P-38. Might drum up more participants.............

Subscribed. The craft paper seems really heavy for a plane this size... I usually use newspaper instead. But it will certainly be strong. Love how you hot-wired the ribs "in situ" instead up building it up a piece at a time. And clamping the wingtips... I'll definitely be stealing that idea. Brilliant!

Originally Posted by warhead_71

Subscribed. The craft paper seems really heavy for a plane this size... I usually use newspaper instead. But it will certainly be strong.

Actually, 30lb basis weight Kraft paper is the same weight as newsprint. The stuff that is usually sold in office supply stores for wrapping packages is 60lb basis weight and it is heavy, but very strong.

Kraft paper is stronger, especially wet, than the same basis weight of newsprint. For our purposes though, newsprint is fine. (Anything that would destroy a newsprint covered wing would probably destroy a Kraft covered wing as well). Newsprint can be had in sheets at many places that sell boxes and moving supplies whereas 30lb Kraft typically has to be ordered in larger quantities on a roll. We use it as packing material for shipping so I have access to it.

Originally Posted by warhead_71

Love how you hot-wired the ribs "in situ" instead up building it up a piece at a time. And clamping the wingtips... I'll definitely be stealing that idea. Brilliant!

I really like the "laser method" for making wings. I'm surprised it's not used more. I don't know who invented it but it's been around for at least 15 years.

Originally Posted by pmullen503

For our purposes though, newsprint is fine. (Anything that would destroy a newsprint covered wing would probably destroy a Kraft covered wing as well). Newsprint can be had in sheets at many places.

Even delivered to your door A destroyed wing would have some intreasting reading

I like this, the 18 was the first plane[ full size] that I flew AF. I also want to build an A26 and might try this method.

Here's a shot of the wing tips after trimming off the excess paper. I sanded off any unstuck paper and rubbed in some white glue to make sure everything was stuck down well. I'll wrap a strip of glass cloth around the edge to make sure the paper doesn't lift in the future and the cloth will add a little more strength to the edge.

The wings were joined with plates of birch veneer on the dihedral braces. The wing holding jig made sure everything stayed lined up. Then I rough cut pieces of solid foam on a bandsaw to fill in the spaces around the dihedral braces. The foam pieces are a drop in fit. The gorilla glue will expand to fill any gaps. I'll sand the center section to shape and cover it with more paper and WBPU.

Normally I would have installed the wiring first but I didn't have enough on hand so I ran strings to pull the wiring through later. I was careful not to let the expanding glue get on the pull strings.

Got started on the fuselage. I'm heat forming the fuselage shells from FFF. I learned of the method from Harpye's builds. The basic principle is to heat the foam in a mold to the point where the foam softens but doesn't collapse. When the foam cools, it retains the new shape. The form acts as the male mold and the tape acts as the female mold. I use a solid form which allows me to build from a three view rather than needing a 3D CAD model and I use an oven to bake the foam rather than a heat gun. The formed shells are very light and rigid minimizing the need for internal structure. You also get a nice smooth surface; except for the seam between the halves, no joints to fill! Once you have the form, you can make multiple copies for your buddies or rebuild it in the future.

I've described the method before in more detail in these theads:
Lockheed Vega
DO-335
Ki-46 Dinah

Here are the highlights:
Start with a pair of backer boards made from 1/2" plywood cut to the side view (minus the thickness of the foam). Rough cut blocks of foam using the cross sections from the 3 view. Glue to them backer boards leaving a gap between the blocks just large enough to slide in the cardboard templates. Sand the form to shape. I drew lines on the cross sections about 1/4" inside the outer edge to account for the thickness of the foam. I don't necessarily sand to this final line on every template. I'm more concerned with getting nice smooth curves and the right shapes. Even on a good 3-view like the one I'm using, there's no guarantee that the cross sections are all correct. When I get close to the final size I stop, slide fresh cardboard into the slots, mark the actual shapes, and from then on I work to made both halves match each other.

Once the mold is done, I cover the film side of FFF with strips of 2" PVC packing tape, overlapping each strip about 1/4". The taped FFF is then wrapped around the form and taped down with more PVC tape. I screwed a 2x3" board to the back side of the form to keep it from warping. It also provides space for the tape to pull the excess FFF as it's heated and the tape shrinks.

The whole thing is baked at 100'C (212F) for 15 minutes in my foam box oven (described in the threads cited above). After it cooled, I trimmed off the excess foam and popped it off the form. The finished halves weighed 85g total. I'll leave the tape on until after the internal structure is added and the halves are joined. The bare FFF is soft and easily dented and keeping the tape on until the last minute keeps it from getting too beat up.

Pat,

Now that is cool . I'm continually amazed at how inventive some of the guys here on RC Groups are.

Steve

Here's a shot of the internal structure. I glued the formers into one side to run the elevator pushrod and work out what I'm going to do with the tail wheel. I was hoping to cram in a small retract in unit but it doesn't look like I'll have enough room. I'll probably end up with a fixed tail wheel.

I plan to make the whole nosecone removable for battery access, probably at the second former. I'm doing the early, short nose version but if it ends up too tail heavy, I'll make a new nose section for the later, longer nose version so I can move the battery farther forward.

A smallish tail dragger like this is going nose over when landing on grass so I'll make a vacuformed or molded fiberglass nose that can be easily replaced when it eventually gets beat up.

Here's shot of the fuselage with the tape removed.

Once the halves are glued together the tape can be removed and the fuselage block sanded smooth. It doesn't take much sanding, just enough to remove the ripples in the FFF and any marks that the tape leaves. The fuselage weighs 122g at this point and less that 2g was removed by sanding to get it smooth.

Note the beach towel covering the bench. The bare FFF is really soft and dents easily at this stage. I gave it a good coat of WBPU to harden it up. Besides making it more dent resistant, the WBPU makes the foam harder than the filler so it can be sanded flush with the foam.

There's a little filling needed here and there along seam. The windscreen area will need more work to get it ready to make the mold for vacuforming the windscreen.

It's looking great!

Len

Subscribed for a cool plane. Will plans be available or are you just working off the three view?